GREENE COUNTY. (361 



already described. Its upper reaches occupy slight depressions in the 

 Drift beds that cover so deep the eastern side of the county, and while 

 at the western margin of the cliff limestone it is bedded in rock, it has 

 wrought out no. deep channel for itself. 



Aside from these principal depressions the general surface of the county 

 is a plain, having an average elevation above the sea of one thousand feet. 

 Throughout the six eastern townships, and in Miami township on the 

 north, the surface is quite uniform— one hundred feet, or one hundred 

 and fifty feet at most, comprising the extreme range of variation in level. 

 The remainder of the county lies, it is true, at a somewhat lower average 

 elevation, but there are insulated summits all through it holding the 

 general level above given. 



By reference to the appended geological map it will be seen that these 

 divisions agree exactly with the great geological divisions of the county, 

 its northern and eastern portions being underlain with the Upper Silu- 

 rian, or cliff limestones ; while from -the western half, though originally 

 present, this formation has been carried away by long-continued erosion, 

 only insulated patches of it now remaining to attest its former extent. 

 It is to be remarked that the occasional summits, already spoken of, in 

 the western half of the county, that are one thousand feet or more above 

 the sea, are in all cases these outliers cr' cliff limestone, to which atten- 

 tion is now called. 



By the removal of the protecting sheet of the cliff limstone, the softer 

 beds of the Cincinnati series have been uncovered, and the wear and 

 waste in them have been much more rapid than in the higher rocks. 



The deposits of the Drift have been spread over all of the county, re- 

 ducing the asperities of the surface and hiding many ancient channels, 

 but after all only modifying and not essentially changing the great fea- 

 tures determined by the underlying geological structure. So that here, 

 as in other counties reported upon, a geological map becomes in great 

 degree a topographical map, the areas of the cliff limestone comprising 

 those districts of the county that have an elevation of a thousand or 

 more feet above tide water, while all other areas belong to the Lower 

 Silurian, or Cincinnati series. 



The lowest land of the county is found on its southern boundary, in 

 the valley of the Little Miami, and ranges between two hundred and 

 seventy-five feet and three hundred feet above low water at Cincinnati, 

 or between seven hundred feet and s^en hundred and twenty-five feet 

 above the sea. The highest land is fortnd in Cedarville and Miami town- 

 ships, along the water-sheds between the Little Miami and Massie's 

 Creek, and the Little Miami and Mad River respectively. It may be 



